The relevant moral theology is not controversial.
Only weighting the risk/benefits is "controversial," though less controversial by the day.
I am quite happy to let Meg and Tradman be teetotalers of both MJ and alcohol (gotta be consistent!) and I will pray for the rescue of their "pothead" loved ones.
I'm not a teetotaler. It's not really a Catholic thing to be.
If I recall correctly, it was Fr. Crane (whom some here don't like, and I understand why) who gave a good comparison, in a sermon, of alcohol and marijuana. Alcohol is used for several reasons. However, it is considered appropriate, by the Church, to use alcohol in moderation. Getting so drunk as to lose control of one's senses is a mortal sin. Getting slightly drunk is a venial sin. However, alcohol if used to just relax is fine. Pot, on the other hand (as Fr. Crane said) is used mainly to get high.
Of course there are medical reasons for using pot, but that excuse is over-used today in order to justify its use, in my opinion. I expect that your opinion, Mark, will be different. That's okay.